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Simulation is a term that has been used for centuries to mean imitation. Simulation has also come to refer to a method of modeling or creating a virtual reality that can range from entirely passive (the 17th and 18th century hyperreal anatomic models of Gaetano Zumbo and Celemente Susini carved in wax and exhibited in La Specola, the Museum of Natural History in Florence) to fully interactive with visual, auditory, and haptic feedback such as those used in training pilots.1,2

Except for educational purposes, imitations are rarely deemed as good as the original. Nevertheless, they are excellent educational expedients and have come to be used in many areas where the risk of error is high. The demand from the master that the pupils “watch carefully and imitate” is heard everywhere skills are taught. Training simulations are assessed on the basis of 2 criteria: the extent to which they re-create a lifelike experience and the extent to which they impart the desired skills. The imitation may not be as good as the original, but it seems like a good way to improve.

The effectiveness of simulation as a training tool turns on the development of a useful, usable, and validated model. The model embodies selected characteristics or features that become “abstractions” of what is being modeled. Thus, the use of latex tubing to teach medical students how to start intravenous lines is a simple and crude simulation. If one adds a layer of simulated skin, the simulation improves. The combination of simulated vein and simulated skin is a “system.” A still more fully modeled system would include an intravenous needle, intravenous tubing, and connectors. The ultimate model might include fluid under venous pressure in the simulated vein. The more complex the system is, the more difficult it is to model.

It is important to differentiate between the model, the system, and the simulation. The system is modeled. The model represents the system. The simulation, in contrast, allows interactions with the system. The range of interactions is finite. It should serve to assist the student in learning and practicing the skills she or he is expected to master. With reference to the system tested in the article by El Ahmadieh et al in this supplement, the model is a model of 3-mm vessels. The simulation involves an anastomosis of these vessels. This was never an easy technique to learn. Indeed, in 1912, Alexis Carrel received the Nobel Prize, the first bestowed on a scientist in the United States, for pioneering the full-thickness triangulated vascular repair technique.3,4

We can expect to see increasing use of simulation in medicine. Although some form of surgical simulation has been in use for centuries, modern surgical simulation evolved conceptually and technically from flight simulation and later applications of similar technologies. Flight simulation is an old idea, developed to save the lives of student pilots. It began almost at the same time as flight itself. Initially, pilots faced the wind in grounded gliders to “feel” the controls. The French Ecole de Combat taught pilot cadets to learn the controls on the ground during World War I with a cut-down Bleriot monoplane. The Sanders Teacher was a tethered aircraft attached to a universal joint that once again taught controls by facing the wind. A device involving a dummy fuselage with pitch, roll, and yaw motions, as well as engine noise and visual input, was described in 1917. The cavalries of most combatant nations also developed mechanical horses to teach riding. The most successful device was the Link Trainer developed by Edwin Link and patented in 1930. The capabilities of simulators broadened hugely during World War II, and in 1948, Curtiss-Wright delivered a full simulator for the Boeing 377 Stratocruisers of Pan American Airlines. This simulator allowed full routes to be flown. It was so realistic that one captain said “from start to finish we had treated the whole exercise as if it were the real thing, and the cockpit was so complete in every detail that we soon forgot that we were not in an aeroplane.” Simulation has become a standard component of pilot training for >8 decades.5,6

Surgical simulation has also been available for years. Dr Richard Satava, a pioneer in the field, has published an excellent historical overview of simulation in surgery and its benefits.2 Satava emphasizes that simulation permits students, residents, and fully trained surgeons to acquire and improve critical skills in a safe learning environment without jeopardizing patient safety.

In a virtual environment, surgeons have “permission to fail.” Safe learning environments and permission to fail have become icons of effective cognitive and skills-based learning. They offer opportunities to learn from mistakes and to focus on specific components of complex skills that individuals master at different rates and in different ways.

Simulation also offers the opportunity for rehearsal. Much as pianists in the past might have practiced at night on muted keyboards to reinforce their motor memory of a piece that they performed the next day, surgical rehearsal allows the surgeon to simulate both the strategy of an operation, from stereotactic radiosurgery to complex spine reconstruction using patient-specific images, and the execution of a procedure.

The anastomosis of small vessels is a technical skill with both cognitive and psychomotor components. Repetition, whether in reality or in a virtual reality, allows many psychomotor skills to become automated, thereby allowing the surgeon to focus more effectively on other aspects of a procedure and potentially increasing situational awareness. Indeed, experts differ from novices most dramatically in having automated most of the psychomotor skills (eg, knot tying) and being able to focus on the cognitive component of an operation, especially the anatomy (perception) and anticipating the next steps (forecasting). In time, it is reasonable to imagine that simulation may be able improve patient outcomes, to increase safety, and to facilitate the introduction and adoption of new technologies.

As the authors have indicated, teaching, learning, and assessment of neurosurgical technique are intimately related. Simulation should be implemented in the context of a validated curriculum for proficiency-based training that incorporates standards for demonstrating proficiency. The simulation should be part of that validated curriculum. It then can be used to benchmark and assess proficiency. For simulation-based learning to be effective, it should be possible to practice or refine the simulation until measured proficiency is achieved.

Simulation has matured since its first application to surgery. In its first phase, surgical simulation imitated flight simulation. It was largely experiential and self-teaching, a better form of programmed learning with psychomotor components.

The second phase saw 2 important additions: validation and curriculum. It became clear that the curriculum was what mattered because simulation needed to address cognitive and psychomotor skills. Simulation needed to have a context and it needed to be validated relative to its training objectives. The emphasis was focused technically on the quality (the “reality”) of the simulation.

The third phase emerged when it became clear that this emphasis was not quite right. It was necessary to focus on proficiency or on the outcomes of training. Although simulation was a good way to improve proficiency, at least in theory, it became clear that simulation could not guarantee proficiency. The learning curve was not the same for everyone. If proficiency was the goal, proficiency had to be proven.

The fourth phase exploited the opportunities for more sophisticated simulation systems and virtual reality displays that arose from advances in computing power. It also led to commercial systems that simulated robotic surgical devices and other important advances in surgery and could be used to train surgeons in new technologies without compromising patient safety.

The next phase is likely to involve not only cognitive and psychomotor simulations but also exercises in team-based collaboration and scenarios such as mass casualty events, surgical rehearsal, and intraoperative crisis response. We can also expected refinements in technology that will offer better simulations, broader applications, and more efficient learning.7-10

The authors are to be congratulated for demonstrating in a straightforward manner the value of simulation and an example of the role simulation can be used to teach surgical technique. More important, they describe the way in which both the process and the outcome could be assessed objectively. To the extent that many surgical techniques can be broken down into relatively simple maneuvers, they can be simulated. Even relatively low-technology simulations can contribute to the achievement and assessment of proficiency. There is little doubt that emerging technologies will make both the psychomotor and cognitive aspects of neurosurgery easier to teach and easier and safer to learn.

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